Effects of light and carbon on phytoplankton production and phyto-microzooplankton trophic interactions in the Baltic Sea: a mesocosm experiment
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
A mesocosm experiment with four triplicated treatments (control, clear carbon, pigment and dissolved organic matter) was carried out to investigate the effects of light (by pigment addition) and carbon (C) on phytoplankton communities and on the grazing pressure of microzooplankton on phytoplankton in the Baltic Sea. Phytoplankton concentration and species composition were determined by using an inverted microscope following the Utermöhl method. In order to measure differences in phyto-zooplankton trophic interactions between treatments, a dilution experiment was performed at the end of the mesocosm experiment. Surprisingly, the results show that light attenuation was beneficial to phytoplankton production while carbon enrichment had negative effects on phytoplankton production, the highest phytoplankton production was in the low light treatment and lowest phytoplankton production was in the clear C treatment. Cyanobacteria were the most dominant group, representing over 95% of the phytoplankton community. Diatoms were the least dominant group, representing less than 5% of the phytoplankton community. Microzooplankton grazing pressure was affected by light attenuation and C enrichment. Grazing pressure was highest on cyanobacteria in the clear C treatment, but chrysophytes experienced low grazing pressure and had high growth rates in the Control treatment where microzooplankton fed selectively on chrysophytes. The least abundant group, diatoms, decreased although they experienced no grazing pressure in the Control and clear C treatments. This experiment resulted in two surprising findings. First, increased light intensity reduced phytoplankton biomass, especially in the clear C treatment, and second, cyanobacteria constituted an important food source for microzooplankton grazers. This study adds to the increasing evidence that light effects can be counterintuitive and that cyanobacteria are not necessarily grazing resistant and can meditate nutrient transport to higher trophic levels.
Place, publisher, year, edition, pages
2015. , 13 p.
phytoplankton, microzooplankton, trophic interactions, light, carbon, Baltic Sea, dissolved organic matter, pigment
IdentifiersURN: urn:nbn:se:umu:diva-98135OAI: oai:DiVA.org:umu-98135DiVA: diva2:782024
Master's Programme in Ecology
2015-01-16, KB5C2, KBC Building, Umeå University, Umeå, Sweden, 12:32 (English)
Liess, Antonia, PhD
Jonsson, Micael, PhD